The present invention generally relates to foil journal bearings and, more particularly, to foil journal bearing retainers.
A foil journal bearing may be a fluid film hydrodynamic bearing and may be used to support a high speed rotating member, such as a shaft. The foil journal bearing, which may be configured to enclose the rotating member, may include a close-fitting, compliant, annular element such as a thin foil encased within a stationary retaining member. Rotation of the shaft within the retaining member may form and maintain a pressurized fluid film between the shaft and the compliant foil. High speed rotation of the shaft may generate a high pressure in the fluid film and this pressurized fluid film may support the load imposed by the shaft.
The compliant foil, such as a top foil, may be secured to the retaining member by edge tabs, also referred to as retaining tabs. The word “compliant” may be defined as “yielding” and a compliant foil may be a foil that is configured to yield, for example, to the pressurized fluid film. A resilient backing member, such as a spring foil, may be disposed between the top foil and the retaining member to accommodate deflections of the foil resulting from pressurization, centrifugal forces and temperature differentials in order to maintain adequate film layer geometry. For some applications, a second compliant foil, such as an under foil, may be disposed between the top foil and the spring foil.
During operation, foil journal bearings can experience high circumferential forces when the fluid film is compromised in an overload condition. These forces are transmitted to the top foil retaining tab and produce a high bending moment and subsequent stress in the top foil that can permanently distort the tab, affect bearing performance and shorten bearing life.
As can be seen, a higher strength retaining design is needed that will prevent loss in bearing performance and shortened bearing life. The design must be simple to minimize manufacturing cost.